Safety pressure-actuated switch



Dec. 3, 1929. McCABE SAFETY PRESSURE ACTUATED swn'cn Filed July 9, 1925 3 Sheets-Sheet A TTORN EY Dec. 3,- 1929. a. E. M CABE v SAFETY PRESSURE ACTUATED SWITCH Filed July 9, 1925 5 Sheets-Sheet 2 m H w E N Dec. 3, 1929. I. E. McCABE SAFETY PRESSURE ACTUATED SWITCH Filed July 9, 1925 5 Sheets-Sheet 3 UV VLNTOR [if M 6452: Mam fi r'l TTORNE V Fiqll UNITED STATES PATENT OFFICE IRA E. MCCABE, OF CHICAGO, ILLINOIS SAFETY PRESSURE-AGTUATED SWITCH Application filed July 9,

This invention relates to improvements in safety appliances and more particularly to a safety pressure actuated switch such as described in my prior pending application Serial No. 19,310, filed March 30, 1925.

In the said prior application a two element electric control is described in the'main circuit for controlling an electrically operated domestic oil burner heater, and this invention is shown and described herein as employed in one element of such a control. In fuel burning systems of this general. character a tilting mercury tube switch is employed to close the operating circuit when the burner flame is ignited and break the said circuit when the flame becomes extinguished, preferably actuated by a pressure or Bourdon tube connected to a thermal coil arranged in proximity to the burner flame whereby the heat of the flame causes the Bourdon tube to expand and rock the switch vwith a snap movement into closed position and upon failure of the flame the coil cools causing the tube to contract and snap the switch into open position. *The improvement made the subject of this application is providing means between the pivoted rocking member carrying the mercury switch tube and the free end of the Bourdon tube whereb the first ex- 39 panding movement of the ourdon tube,

when the pressure therein reaches a certain degree, will actuate the switch mechanism to 'rock the switch tube into closed position and allow further expanding movement of the Bourdon tube therebeyond. If the pressure within the Bourdon tube becomes too great there is danger of injuring or destroying it and this invention contemplates mechanism whereby the expansion of the Bourdon tube as it approaches the danger limit will actuate the switch mechanism to rock the tube switch to open position so that the flame is extinguished when its heat becomes too great for the safety of its-control and as thermal coil cools and theBourdon tube contracts it returns the actuating'mechanism of the'switch to the first relation to the tube in the open position; i J

With these and other objects in view, reference is made to the accompanying drawing 1925. Serial N0. 42,405.

which illustrates a form of this invention as embodied in an electrically operated fuel burning system of the character described. However this invention is not limited-to this particular embodiment as it can be applied to any other use of tilting mercury tube switches actuated by any form of prime mover instrumentality.

In the drawings:

Figure 1 is a view in front elevation of one form of a pressure actuated snap movement mercury tube switch, with cover removed and the mercury switch tube shown in dot and dash lines in open position as constructed in accordance with this invention.

Figure 2 is a detail view of the parts as shown in Figure 1 with the front plate and mercury switch tube removed.

Figure 3 is a similar View showing the position assumed by the moving parts upon normal expansion of the Bourdon tube in which the switch tube is in closed position.

Figure 4 is a similar view showing the position assumed by the moving parts upon further expansion beyond the normal and approaching the danger limit of the Bourdon tube in which the switch tube, has been thrown to open position.

Figure 5 is a view similar to Figure 1 of another form illustrating a modification in the actuating mechanism.

Figures 6, 7 and 8 are views illustrating this form of actuating mechanism in positions corresponding to Figures 2, 3 and 4.

Figure 9' is a view in vertical section illustrating the. application of this invention to a stack control.

' Figure 10 is a view in end elevation of the thermal coil shown in Figure 9.

Figure 11 is a view "in front elevation of Figure 9, with the casing cover removed.

Figure 12 is similar view of a modification of Figure 11:

The embodiment of this invention, as illustrated, shows in Figure l a casing 1 in which is mounted apressure' or Bourdon tube ,r

2 having, a connection 3 to the source of pressure and leading in wires 4 and 5 from a commercial or other electric circuit connected to binding posts 6 and? which in turn are connected by flexible leads 8 to the terminals 9 entering one end of a mercury switch tube 10, shown in dot and dash lines, which switch tube is mounted on a snap movement mechanism generally similar to that shown and described in my prior pending application Serial No. 585,698, filed September 1, 1922, which is actuated by the expansion and contraction of the Bo'urdon tube in response to the variations of pressure. Improvements have been made in the snap movement actuating mechanism whereby in the normally contracted position of the Bourdon tube the mercury switch tube is positively held in tilted position with the mercury accumulated in the end opposite the terminals so that the switch is open and upon the expanding of the Bourdon tube the mercury tube is rocked to a degree sufiicient to cause the mercury to flow into the end containing the terminals and close the circuit therethrough in which position it is positively held until the Bourdon tube either contracts to the first position, rocking the switch tube to open position, or expands beyond the safety limit whereupon such further movement the mercury switch tube is snapped back into open position and positively held there while the moving parts,

as the Bourdon tube contracts, assume their first relation to the mercury tube. As aforesaid this mechanism is particularl adapted to devices in whichthe closing the electric circuit is directly responsive to the pres sure, or temperature causing the pressure,and in which the pressure reduces to normal upon the breaking of the circuit. The switch snap mechanism may be said to perform three functions; namely, normally holding the switch in open position, upon pressure increasing closing the circuit and holding the switch in closed position; upon pressure becoming too great throwing the switch to open position and holding it in open position and as pressure decreases allowing the moving parts of the mechanism to assume the first or normal position without afiecting the switch. The relation between the switch mechanism and Bourdon tube is adjustable in the same manner as previously described in my prior application Serial No. 538,916,1iled February 24,1922, so it need not be described here and therefore the adjustment is not particularly illustrated.

The switch operating mechanism is mounted on a base plate 11 mounted on the rear wall of the casing and includes a rocking member 12 in the form of a bracket plate mounted to rock on a central pivot extending outward from the base plate, having a right angular extension 13 from the upper side .upon which the mercury switch tube is carried. An operating member 14 is mounted on a pivot therebelow extending from the base plate and having a link 15 pivotally mounted near one end having a roller connection 16 extending on the opposite side of its pivot from the link depends therebelow and is provided with a slot in which is adjustably and pivotally mounted a safety arm block 19. An operating lever 20 is pivoted to the base plate at one end approximately in line with the rocking member with a post 21 extending outward from the base plate between the rocking member and operating lever pivot and another post 22 of similar height extends outward from the base plate on the outer side of the roller carrying link to which posts a front plate 23 is secured by screws entering the posts 21 and 22 which plate also engages and rigidly maintains the outer ends of the respective pivots extending from the base plate.

A mercury switch tube 10 having terminals 9 entering one end is carried between clamps preferably extending downward from a plate at adjustably secured upon the right angular extension 13 of the rocking member, which switch tube and carrying plate is shown in dot and dash lines in Figure 1. The rocking member 12 on the side adjacent the operat ing lever is provided with two spaced apart projecting arms 25 extending on either side of the post 21 carried on the base plate between said member and operating lever pivot adapted to engage said post to limit the rocking movement of said member, the opposite side being provided with angular converging edges 26 which would normally meet in a plane through the rocking member pivot parallel to the switch tube carrying extension 13 but before the edges meet they are cut out as shown at 27 to receive roller 16 mounted between the free ends of the side plates forming the pivoted link 15 which side plates at the other end engage on opposite sides of the operating member 14 and rotate is provided with a bent back projection 29 adapted to'travel over an arcuate plate 30 secured upon the front plate 23, as shown in dot and dash lines. The projection forms an indicator pointer and the portion of the plate 30 over which it travels is provided with a scale to indicate the pressure, or temperature generating the pressure, within the Bourdon tube causing the movement of thefree end of the operating lever through the opeating link as the Bourdon tube expands and contracts. A safety arm block 31 is pivotally mounted on the free end of the operating lever adapted to travel under the indicator index plate 30. A safety arm, 32 preferably in the form of a rod, as shown in Figures 1, 2, 3 and 4, is mounted to travel through the safety arm blocks 19 and 31 pivotally carried on the operating member and operating lever, respectively. The rod is adjustably secured in block 19 by a set screw 33 andis mounted to slide through block 31 with its end enlarged to engage the block and limit the movement of the operating member away therefrom. A friction contact is provided between block 31 on the lever and the rod 32 preferably in the form of a spring arm 34 secured to the block with its free end pressing upon the arm, which spring is of sufiicient length as theBourdon tube contracts to normal to first engage the safety arm block 19 on the operating member 14 and then rotate that member about its pivot until the moving parts are in the position shown in Figures 1 and The operation of the device is as follows:

There being no pressure in the Bourdon tube, the tube is contracted which through link 28 has moved the free end of the operating lever to cause the operating member to be rocked on its pivot through contact of the spring arm 34 with the safety block 13 thereby elevating the free end of link 15 cans ing the roller carried thereby to engage in the cut out portion of the rocking member and rotate it about its pivot until the upper arm 25 engages the post 21, thereby rocking the mercury switch tube to open position. As pressure accumulates in the Bourdon tube it expands causing its free end to move toward the side wall of the casing and as it increases this movement transmits a similar movement to the free end of the operating lever 20. As the operating lever moves outward the indicator pointer travels over the scale on the arcuate plate and at the same time exerts a pull on the safety block 19 on the operating member 14 through the frictional engagement of the spring arm 34 of the block 31 upon the rod 32 thereby rocking the operating member upon its pivot causing the pivoted end of the link 15 to descend which through its roller 16 engaging in the cut out portion 27 of the rocking member 12 causes this member to rotate upon its pivot rocking the mercury switch tube until the end containing the terminals is lower than the other end and the merciiry flows about the terminals and closes the circuit.

The rotation of the rocking member 12 is limited by contact of the lower arm 25 with the post 21 which holds the switch in closed position as long as there is suflicient pressure in the Bourdon tube. This closed position is shown in Figure 3 of the draw-- ing; If the pressure in the Bourdon tube decreases then the parts return to the position illustrated in Figure 2, upon contraction of the tube. On the other hand, should the pressure increase beyond that necessary to rock the switch tube to closed position the further outward movement of the free end of the Bourdon tube causes the safety block 31 on the operating lever 20 to ride over the safety arm rod 32 and this pull of the Bourdon tube overcomes the friction between the spring arm 34 carried by safety block 31 and the rod 32 fixed to the safety block 19 on the operating member. It is necessary to provide the spring 17 for the roller carrying link 15 of greater tension than the friction between the arm 32 and spring arm 34 to allow independent movement of the block As the pressure decreases the safety block 31 through the friction of the spring arm 34 upon the safety arm rod 32 causes the operating member to rock and thereby return the rocking member to the position shown in Figure 2.

Should the pressure in the Bourdon tube continue to increase beyond the safety limit the tube will be injured or destroyed. To

prevent such an occurrence, the safety arm rod is so adjusted in safety block 19 of the operating member that before the pressure reaches thecrit-ical danger limit of the tube, the enlarged end of the safety arm rod 32 is engaged by the safety block 31 on the operating lever and further outward movement is then imparted to the operating member 14 which causes a downward pull on the link 15 overcoming the tension of the spring 17 causing the rollerlti to ride over the lower edge of the cut out portion and engage the angular lower edge 26 of the rocking member 12. The pressure of the roller against the angular edge causes the rocking member to snap into the position shown in Figure 4 with the upper arm 25 in engagement with the post 21, which position of member 12 is the same as shown in Figure 2, and the circuit is broken.

As the Bourdon tube contracts from this extreme position the safety block 31 of the operating rod rides back over the safety arm rod 32 overcoming the friction between the spring arm 34 and safety arm rod 32 until the free end of the spring arm 34 of the block 31 engages the safety block 19 of the operating member 14 which then imparts an upward movement to the roller carrying link 15 causing the roller 18 to ride up over the inclined edge and into the cut out position 27 of the rocking member 12, bringing the moving parts of the mechanism into the original position, illustrated in Figures 1 and 2, without moving the mercury switch tube from its open position.

The form' illustrated in Figures 5 to 8 inelusive operates in the same general manner.

the slot of the operating member. A tension spring 38 anchored preferably at one end to the operating lever pivot, or at that end to the safety link and at the other end to the member 37' on the operating member which spring is of less tension than that of' the roller carrying link spring 17 and normally holds the innermost end of the slot of the safety link against the pivot member 37 of the operating member. This slotted pivoted safety link 35 and spring 38 act in the same manner as the pivoted safety arm blocks,

safety arm and friction spring shown in'the first four figures of the drawing. In the normal position the mercury switch tube is. in the open position as shown in the dot and dash lines of Figure 5, with the operating mechanism parts as shown in Figure 6. As the Bourdon tube expands the safety link 35, held'by spiing 38 with the innermost end of slot 36 against the operating member pivot 37, rocks the operating member and related parts to the position shown in Figure 7 and upon further expansion of the Bourdon tube the spring 38 allows the slotted end of the safety link to travel over the fixed member 37 which is so adjusted on the operating member 14 that as the danger limit of the Bourdon tube is approached the outer end of the slot 36 engages the member 37 and throws the, parts into the position illustrated in Figure 8, thereby breaking the circuit through the mercury switch' tube 10. The

springs 17 and 35 as the tube contracts return the moving parts to the normal position illustrated in Figure 2 without closing the circuit, as the inmer end of the slot engages the member 37.

There is this difference between the forms shown in Figures 1 and 5. In the construction illustrated in the first four figures, the

first movement outward of the operating lever 20, through the friction between spring arm 34 and safety arm rod 32, rocks the bracket plate 12 from the position shown in Figure 2 to that shown in Figure 3, further outward movement of the operating lever.

overcomes the friction but the spring 17 retains the rocking bracket plate 12 in the position shown in Figure 3 until the safety arm block 31 engages the enlarged end of the safety arm 32 and then further outward movement of the operating lever 20, having a direct engagement with safety arm block 19 through therod 32, overcomes the tension of spring 17 and snaps the rocking plate -12 into the position shown in Figure 4. However, if at any point intermediate the position shown in Figure 3 and the engagement of the enlarged end of the safety arm-rod the operating lever ceases in its outward movement and begins to move inward, then this inward movement is transmitted at once, through the friction between the spring arm 34 and safety rod 32, to cause the operating member to rock and immediately return the rocking bracket plate 12 to the position shown in Figure 2, thereby breaking the motor circuit. In the construction illustrated in Figures 5 to 8, inclusive, the safety link 35, with the slot 36 engaged by the member 37 carried on the operating member, through the spring 38 upon the first outward movement of the operating lever tilts the rocking bracket plate 12 from the position shown in Figure 6 to that shown in Figure 7, the spring 38 holding the inner end of the slot 36 against the member 37. Upon further outward movement of the operating lever, the tension of the spring 38 is overcome and the safety link slides over the member 37 until the outer end of the slot engages it and then on further movement in the same direction overcomes the tension of. the spring 17 and rocks the operating member to snap the rocking bracket plate 12 to the position shown in Figure 8. However, should the operating lever cease its outward movement, after having rocked the parts to the position shown in Figure 7, at a point intermediate the length of the slot 36 and begin a movement in the opposite direction, theinward movement will not rock the operating member until the inner end of .the slot 36 engages the member 37. Therefore the motor circuit is not broken until the inner end of the slot 36 rocks the operating member 14. It is to be noted that should the spring 17 fail by loss of ten sion or destruction, the weight of the mercury switch tube 10 carried on the extension 13 at one side of the pivot of the bracket 12 will immediately rock'the bracket plate to the position shown in Figures 2 and 6, thereby immediately breaking the motor circuit. Should the spring arm 34 or the spring 38 fail to operate, the parts would remain in the position shown in Figures 2 and 6 or,

should their failure occur after leaving the position shown in Figures 3 and 7, the parts would be returned to the first position by the safety rod or safety link when the danger limit is approached .or, if the operating le-,

after having snapped the switch tube into open position through the safety rod or link,

as shown in Figures 4 and 8, then the parts would not return to normal and the mechanism would be inoperative to close the circuit until the cause had been removed.

As stated in the introduction, While a Bourdon tube and a snap movement switch mechanism are shown in the eight figures other types of prime mover instrumentalities with other types of switch mechanisms an be employed to accomplish. the same results.

For instance, a stack control, such as shown 1n 'Figures 9 and 10, is adaptable for the prime mover instrumentality, in which case the casing 1 would preferably be mounted on or adjacent the stack 40. and is preferably carried on the sleeve 41, projecting from both sides the plate 42 secured to the stack, with a thermal or bimetal coil 43 surrounding the portion within the stack having one end secured to'a post 44 carried on the stack plate and the other end fixed to a rotatable shaft 45 extending through the sleeves and passing through a cap 46 on the interior of the casing. The temperature in the'stack upon increasing will cause the thermal coil to expand thereby imparting a rotating movement to the shaft 45 in one direction and upon dey, creasing will cause the shaft 45 to rotate in I no the opposite direction which movement is readily substituted for that of a Bourdon tube to impart thenecessary movement to theop er-ating lever20, as hereinbefore described.

The stack control illustrated in Figure 9' also shows a switch mechanism in Figures 11 and 12 in which a resilient strip 48 is secured atone end to a block 47 of fibre, or other insulating material, adjustably secured by the set screw 49 upon the end of the shaft 45 projecting within the casing, A contact member 50 is mounted onthe free end of the resilient strip adapted to be engaged with a corresponding contact member 51 mounted upon a block 52 of fibre, or other insulating material, carried on the rear Wall of the casing, with the binding posts 6 and 7 to which the leading in wires from the commercial or other current are connected having flexible connection53 to the end of the strip secured to the block 47 and block 52, respectively. In Figures 9 and 11 a fixed post or abutment 54 is provided extending outward from the rear Wall of the casing in the path of the resilient strip 48 intermediate its ends. The block 47 is so adjusted uponthe rotatable shaft 45 and the abutment 54 is so located that when the stack is cool. the contact members 50-and 51 willbe separated or in the open circuit position, as shown in full lines in Figure 11. As the temperature in the stack increases, as upon the ignition of the burner flame, the thermal coil will cause the shaft 45 to rotate, bringing the contacts 50 and 51 together and close the circult and upon further increase in temperature to approaching the danger limit, or at a predetermined creases the parts will resume the relations shown in full lines. Figure 12 illustrates a Wiping contact arrangement in which the abutment is omitted and the free end 55 of p the strip is bent at an angle and carries the contact 50 with contact 51 carried on the under side of block 52. The normal position of the parts are shown in full lines. Upon rotation of the shaft 45 the contacts 'will be brought into wiping contact and upon further movement the contact 52 Will wipe acrossand beyond the face ofcontact 51 to the position shown in dotted lines and the circuit broken. Upon cooling of the stack the parts will be returned. tonormal. The expansion and contraction movement of the free end of a Bourdontube is also readily adaptable to rock the block carrying the strip 48.

lit is to be safety switch mechanism may be most advantageously used in connection with a domestic oil burner system in which the oil and air are both furnished by'an electric motor with this safety mechanism in the main motor circuit, however, it is just as applicable to any other type of fuel burner system employing an electrical control with this safety mechanism in the control circuit. In the preferred type of fuel burner system it is customary to employ a room thermostat for actuating the burner mechanism as Well as a boiler control, this improved safety switch being an additional element to such controls.

W hat if claim is:

1. An electrical safety control switch including a moveable member forclosing the circuit therethrough, an expansible and contractable prime mover for operating said movable member to close and break the circuit actuated by external conditions, and

.means operable after the circuit has been further understood that this tinned movement of the prime mover in the same direction. 3. An electrical safety switch including a moveable member for closing the circuit therethrough, an expansible and contractable prime mover for said member actuated by external conditions normally maintaining the member in open position and upon a normal change of conditions moving said member to close the circuit and maintaining it in closed position, and means actuated by an abnormal change of conditions causing further movement of the prime mover in the same direction to operate said member to break the circuit.

4. An electrical safety switch mechanism including a moveable contact, an expensible and contractable prime mover therefor actuated automatically-byexternal conditions to close and break the circuit normally maintaining the contact in open position, adapted upon'a predetermined change in conditions to close the circuit, maintaining the contact in closed position, upon a further predetermined change in conditions actuating the prime mover in the same direction to break the circuit and maintain the contact in open position, and upon return to normal conditions to return the contact to the first position.

5. An electrical safety switch mechanism including a moveable contact and means operated automatically by an expansible and contractable prime mover actuated by external conditions to normally break the circuit and remain in open position, upon a predetermined change in conditions to close the circuit and remain in closed position under such conditions, 'upon further predetermined \change. in conditions actuating the prime mover in the same direction to break the circuit and remain in open position, and upon the return of conditions to'normal at any time to return the contact actuating means from the position occupied by it at the time of the change to the first position.

6. An electrical safety switch mechanism including a movable contact member for making and breaking the circuit, an expansible and contractable member operatively connected thereto, means normally maintaining the contact in open position actuated by a predetermined expansion of said member to move the contact into closed position and in that position allow further predetermined expansion and thereafter to move the contact into open position and upon contraction toward normal from any amount of expansion to return the contact to the first position upon initiation of contraction.

7 An electric switch safety operating mechanism including a mercury switch tube adapted to make and break the circuit therethrough carried in a rocking member normally in open position, a prime mover, and means between the prime mover and rocking 'member for normally holding the switch in open position and upon normal movement of the prime mover, to rock the switch tube to closed position and hold it in such position during a predetermined amount of abnor mal movement of the'prime mover'and upon continued abnormal movement therebeyond to throw the switch tube to open position and hold it in that position until the ,prime mover returns to normal.

, 8. An electric switch safety operating mechanism including a mercury tube switch adapted to make and break the circuit therethrough, a rocking member upon which the switch tube is mounted, an operating lever adapted to be actuated by a prime mover, and actuating means between the operating lever and rocking member normally maintaining the switch in open position and upon movement of the lever to first rock the switch to closed position, then, allow further movement of the lever, and upon continued movement in the same direction to a predetermined point to throw the switch to open position.

9. An electric switch safety operating mechanism including a mercury tube switch adapted to make and break the circuit therethrough, a rocking member upon which the switch tube is mounted, an operating lever adapted to be actuated by a prime mover, and actuating means between the operating lever and rocking member normally maintaining the switch in open position and upon move ment of the lever to first rock the switch to closed position, then allow further move ment of the lever, upon continued movement to a predetermined point to throw the switch to open position, and, while, maintaining the switch in open position, allow the actuating means to return to normal upon movement of the operating lever to normal position.

10. An electric switch safety operating mechanism including a mercury tube switch adapted to make and break the circuit therethrough, a rocking member upon which the tube is mounted, an operating lever therefor. a Bourdon tube, an operative connection between the free end of the Bourdon tube and the operating lever, a pivoted operating member, a spring pressed roller carrying link pivoted atone end of the operating lever adapted to engage the roller with the rocking member, a slidable connection between the operating member and operating lever, means upon the sliding connection causing the operating member to be actuated by the operating lever to rock the switch tube to closed position upon normal expansion of the Bourdon tube, then' allow a further independent movement of the operating lever in the same direction and upon further abnormal expansion of the Bourdon tube to actuate the operating member to return the rocking member to open' position and an indicator pointer upon the free end of the operating lever brated to indicatethe degrees of the power causing the expansion of the Bourdon tube.

IRA E. McCABE.

adapted to travel over a scaled plate cali- 

